Method for detecting relative humidity of drycleaning solvents

ABSTRACT

IN A DRYCLEANING SYSTEM, A METHOD FOR RAPIDLY DETECTING RELATIVE HUMIDITY OF DRYCLEANING SOLVENT IN THE WASHING CHAMBER COMPRISING POSITIONING ADJACENT TO THE WASHING CHAMBER AT THE OUTLET CONDUIT A CONDUCTIVITY DEVICE THROUGH WHICH ALL OF THE SOLVENT FROM THE WASHING CHAMBER PASSES, SAID CONDUCTIVITY DEVICE COMPRISING AN OUTER TUBULAR ELECTRODE AND A CONCENTRICALLY MOUNTED INNER ELECTRODE.

Feb. 9, 1971 MICHAELS ETAL 3,561,917

METHOD FOR DETECTING RELATIVE HUMIDITY OF DRYCLEANING SOLVENTS Original Filed Dec. :5, 1963 6 SEVS/T/VE RELAY WASHER PUMP BUTTON TRAP 14 lIllltlllllllllll-gi 5 5 /7///// //A I6" /5 I50 R 2 4 I I5 24 23 INVENTORS. EDWIN B. MICHAEL-S CLAYTON A. WETMORE THOMAS IV. MURPHY ATTOR/VE United States Patent Int. Cl. D061 1/10; G01n 27/10 US. Cl. 8-14 4 Claims ABSTRACT OF THE DISCLOSURE In a drycleaning system, a method for rapidly detecting relative humidity of drycleaning solvent in the washing chamber comprising positioning adjacent to the wash ing chamber at the outlet conduit a conductivity device through which all of the solvent from the washing chamber passes, said conductivity device comprising an outer tubular electrode and a concentrically mounted inner electrode.

This is a division of application Ser. No. 327,649 filed Dec. 3, 1963.

The present invention relates to methods and apparatus for efficiently drycleaning fabrics, garments and the like. More particularly, it relates to processes of the type which are carried out by the careful regulation of water absorption on garments of fabrics to be drycleaned in controlling relative humidity in a washer zone within predetermined critical limits. Still more particularly, the invention is concerned with novel conductivity equipment adapted to ensure enhanced cleaning efficiency of a drycleaning solvent.

It is well known that the presence of moisture in a drycleaning solvent is necessary for the removal of various types of soils and stains from a garment during the drycleaning operation. However, the amount of moisture picked-up by the exposed garment to be cleaned materially affects the success or failure of the cleaning process. For instance, if there is too little water content present, there will be little if any removal of soils and stains. To effect such satisfactory removal, additional spotting operations are required. These unduly increase the cost of the operation. On the other hand, too much moisture content will also affect a garment insofar as shrinkage, wrinkling and color loss are concerned. For best overall results, the relative humidity within both the solvent and the garment has been maintained at from about 55% to about 75% with various degrees of success. As a practical matter, it has been demonstrated that the solvent relative humidity and moisture pick-up by the garment must be accurately established and maintained within the aforementioned relative humidity range. Otherwise, the efficiency of the cleaning operation is markedly low.

Many attempts have been made in the prior practice 2,949,336, issued to Michaels et al. However, it has been recently found that the reliability of the sensor therein can :be adversely affected by foreign substances usually introduced into the washing zone by commercially available detergents containing a variety of calcium or amine salts. To develop a universally acceptable technique suitable for all detergent-charged solvent systems would, therefore, be highly desirable.

One known technique is to measure the conductivity of the drycleaning detergent-charged solvent. A conductivity device for this purpose that recently gained commercial prominence is described in the US. Letters Pat. No. 2,913,393, issued to Mathews et al. At best, the conductivity device defined therein accurately measures the relative humidity of a filtered solvent water system external to the washing zone. Unfortunately, rapid and simultaneous detection of relative humidity within both the cleaning solvent and the garments to be cleaned cannot be readily achieved utilizing the particular conductivity device described in the aforementioned patent.

Continued expenditures of time and treasure have been made in an attempt to devise a drycleaning system in which relative humidity (RH) within the washing unit can be determined accurately regardless of detergent type in the solvent. Accordingly, this invention has for its object the provision of overcoming the difficulties of the prior art by utilizing a novel trouble free conductivity device which, when positioned judiciously in the drycleaning system, can accurately and rapidly cause to be detected any change in relative humidity with the washer unit zone.

To achieve the objective of accurate control and detection of Water addition both to soiled garments and to a commercial drycleaning solution comprising a detergentcharged organic solvent, there is provided a novel conductivity device positioned immediately adjacent to the washer unit and through which dirty of un-filtered solvent flows. In this manner, the conductivity device acts substantially as an analogue of the garment surface so as to predict the terminal relative humidity of the garment under a constant or regulated rate of moisture addition.

It has been unexpectedly discovered that a conductivity cell comprising a housing as an outer electrode and a spaced-apart, concentrically positioned inner electrode when placed directly and immediately adjacent to the washer or washing zone acts as an effective sensor of the humidity state of a solvent passing immediately from the washer to the filter. This is surprising because conductivity devices as employed in the prior practice cannot be positioned immediately adjacent to the washer due to the presence of lint or other foreign bodies in the solvent. These impurities normally inactivate conductivity devices rendering them substantially useless. For this reason, conductivity devices where employed have gen erally been remotely positioned with respect to the garments in a washer at a point receiving filter or lint-free solvent. Therefore, according to the process of the present invention, conductivity devices as defined, when placed adjacent to a washer zone rapidly sense any change of relative humidity within the washer by sampling all the solvent as it issues from the washer.

In general, the conductivity device of the present invention comprises an outer tubular electrode as the housing and a concentrically mounted inner electrode. The annular space between the electrodes permits all the dirty solvent emitting from a washer zone to freely flow therethrough. Thus, lint or any foreign matter will not clog the conductivity device, rendering it completely operative as an indicatdr of moisture in the solvent. Significantly, the device rapidly detects excess water which by-passes the garments and determines how the rate of excess water reflects the humidity level of the garments being cleaned. A conductivity device of the present invention, therefore, senses accurately the moisture state of both solvent and garments by detecting changes in moisture of the entire drycleaning solvent as it passes into and through the device, the device being stable to all detergents and unaffected by lint or foreign matter.

It has been further discovered that under conditions of constant rate of water addition, the rate of moisture pickup is inversely proportional to the moisture content of the garment. With a constant proportion of the water input to the solvent input, the regain of the garment establishes the rate of absorption of moisture. Consequently, the introduction of excessive quantities of water to the washer is prevented, since the conductivity device responds more rapidly than does the garments.

Conductivity determinations in commercially available drycleaning solvents depend upon resistivity parameters which are not observed in other conductivity determinations. For instance, the specific resistivity of tap water is about 14x10 ohms, whereas a drycleaning solvent has a specific resistivity of the order of 10 ohms. To thus obtain measurable parameters in media of the order of megohm resistivity, it is found necessary to use electrodes having cell constants of greater than and preferably up to about in order to employ resistance sensitive meters or relays that operate efficiently in the required megohm resistance range.

To achieve cell constants of this latter order of magnitude, conductivity cells were previously designed by positioning the electrodes of the cells in close proximity. Hence, conductivity devices could be used in areas through which only clean or filtered solvent flowed, for otherwise the accumulation of foreign matter between the electrodes would cause bridging of the cells. In addition, the normal rate of flow of the solvent had to be reduced because the force of solvent flow past a cell having closely positioned electrodes rapidly distorted the cell. Nonetheless, it remains advantageous to position the conductivity cell in a solvent conduit adjacent to the washer and that such cell be of unique structure so as to permit the free flow of contaminated or dirty solvent and not occlude the lint, filter powder, soils and other foreign particles inherent to the drycleaning operation.

It has been found that such a cell can be made with usable cell constants of at least i or greater, by constructing (a) the outer electrode as a continuous section of the pipe conduit and (b) an inner electrode spacedapart by an inert non-conductive spacing element, the inner electrode preferably being a solid rod. Surprisingly, the inner electrode can be of significantly smaller surface area than the outer electrode with substantially less decrease of cell conductivity than would be expected and that such inner electrode can be placed in the conduit without substantial decrease of the cross sectional flow area of the passing cleaning fluid.

Conductivity cells of the present invention are constructed so that the internal radius of the outer electrode is at least 50% larger or more than the radius of the inner electrode, and preferably 100% larger. Under these circumstances, the cell constants are influenced in media of low conductivity by the area of the relatively larger electrode and the cross-sectional area of the smaller electrode which will displace less than of the crosssectional area of the conduit system while simultaneously not impeding the flow characteristics of the solvent.

The invention will be described with reference to the accompanying drawings in which FIG. 1 refers to a flow sheet that constitutes one mode for practicing the invention, 'FIG. 2 is one embodiment of a conductivity device, partly in section and partly in elevation and FIG. 3 is a preferred embodiment of an alternative conductivity device in cross-section.

Referring to the drawings, a washing chamber in FIG.

1 is generally designated at 1. Filtered solvent is fed through line 2 and then returned through an opening 3 into the washing chamber 1 to complete the cycle. The conductivity device generally designated 4 being detachably mounted and directly connected to the line 2 by means of suitable couplers 5. The conductivity device is linked to the resistance sensitive relay 6 through wire leads 7 attached to the conductivity device 4. A relay 6 then actuates solenoid valve 8 through wires in a cable 7a when the resistance of the conductivity cell is above a predetermined controlling value. Thus, water at a predetermined rate is introduced into the solenoid valve 8 through line 9 and will flow through a conventional flow measuring and controlling device 9a through line 919 into line 2. By spraying the water into line 2 through an atomizing nozzle 10, intimate mixing with solvent will occur readily. In the meantime, contaminated solvent in the washing chamber is withdrawn through conductivity device 4, and button trap 12 by operation of pump 13 and fed through filter 147 Clean solvent is next returned through line 2 to the washer zone at 1. Proper terminal RH is thus quickly established in the washer, since the conductivity of the solvent is sensed as soon as it issues from the washer.

In FIG. 2, the conductivity device attached (as in FIG. 1) to the main conduit through couplers 5 is shown in elevation and in section as comprising an outer tubular electrode 4, an inner concentrically mounted electrode 411 attached to the outer electrode by means of suitable metal screws '15 separated from the electrode 4 by utilizing inert plastic insulating separators 16. The screw 15 passes through a suitable washer 15a and is inserted into and passes through inert plastic separators 17. This ensures that the two electrodes are maintained in an apartspaced relationship and electrically inert with respect to each other. Lead wires 18 and 19 are attached to the inner and outer electrodes, respectively, and are linked to a resistance sensitive relay (not shown). The arrows indicate the flow of fluid.

In FIG. 3, there is shown in cross section a preferred embodiment of the conductivity device in the form of a T-pipe conduit 20 in which a portion of an inner solid electrode 4b of radius R is threaded and inserted at 21 into a partially internally threaded L-shaped electrically inert plastic plug 22. The plug and inner electrode assembly is next inserted at internally threaded horizontal T pipe at 23 and matching external threads of the L plug until the assembly fits snugly in the T pipe opening at 24. Lead wires 25 and 26, connected to terminals 27 and 28, respectively, are attached to a resistance sensitive relay (not shown). Contaminated solvent enters port 29 and exits through port 30. Lead wire 25 is connected to the external electrode 4c having an internal radius R The use of the conductivity cell in the solvent area leaving the washing chamber normally presents difficulties with respect to cell contamination by solid material leaving the washing zone. In the normal practice in drycleaning it is customary to add large quantities of filter powders to the washer zone during and prior to the cleaning cycle. It is for this reason that the cell defined by FIG. 3 is a preferred embodiment because it is self-cleaning in operation. It is believed this effect is achieved due to flow, turbulence or venturi effects. Thus, the resultant non-air binding condition does not give false conductivity values.

To demonstrate the relationship between the spacings of the electrodes as shown in either FIG. 2 or FIG. 3, cells comprising an etxernal electrode are constructed, for instance as shown in FIG. 3, from a standard 2 /2 inch pipe T for use in a 2 inch standard pipe conduit and having an internal radius (R equal to 3.7 cm. These are compared to cells having varying radii (R of an internal electrode ten centimeters in length. Data as to cell constants, K, and percent cross'sectional area change within the solvent pipe conduit, are noted and tabulated in Table 1 below:

TABLE I.-CONDUOTIVITY CELLS COMPARED [Internal radius of external electrode (R =3.7 cms.]

Radius of internal electrode (R1 in cms.)

R=1.3 R1=l.7 R2=2.0 R1=3 Ratio of R /Rz 1/2. 75 1/2. 20 1/1. 85 1/1. 23 Cell constant (K) calculated:

X21rRl Cell constant, K,* found (in drycleaning solvent having a 500 megohm specific resistivity) 1/110 1/260 l/290 1/420 Increase of conductivity from calculated cell constant in drycleaning solvent 3X X 4X 1. 5X Cell constant (I?) found in tap water having a 14,000 ohm specific rcsistivity 1/ 68 1/ 75 1/ 137 1/300 Decrease of conductivity in water from constant in drycleaning solvent 0. 6X 0. 3X 0. 5X 0. 7X

K is determined by measurement of cell in same medium against a known coll.

From the data in the above table, it will be seen that it is feasible and practical to decrease the size of the inner electrode (R This permits maximum solvent flow and clearance to be maintained with attendant less decrease in overall conductivity through the cell than is expected from the surface area of the inner electrode.

The construction or design of the drycleaning system which includes the addition of water to solvent at a constant rate to the rate of solvent circulating through the washer zone and the measurement of moisture in the solvent immediately after leaving the washing zone leads to certain significant advantages in control of the moisture level of garments in the washer zone when the method of measuring the moisture content of the solvent is rapid and not subject to hysteresis loss in the transducer or sensor. Because conductivity measurements of the solvent media are direct measurements of the solvent state, they are by their nature measurements free from any transducer lag. It has been observed that the addition of solvent at constant moisture content to the washer containing garments results in a solvent mixture which exits the washing zone containing decreased water content. This decrease is an inverse function of garment regain, which regain is defined as the moisture content of the fabric as a percentage of moisture content at equilibrium in a 100% RH environment.

For instance, if a solvent detergent mixture containing a 1% anionic detergent is circulated through the washing zone and water is injected to the solvent at a constant rate of 8 ounces per minute per 3000 (gallons per hour) of solvent, it is calculated that the solvent enters the washing zone containing 0.14% water where the garment regain is less than about 30% and the solvent leaving the washer will contain about 0.03% water. However, when the garments reach a regain value of about 60% the solvent leaving the washer will contain a moisture content of 0.10%. It can be seen that this differential effect in moisture content is magnified during the washing cycle as the solvent circulating through the filter and back to the washer without any moisture control tends to increase in moisture content. The use of a conductivity measurement device as a transducing device at the point where the solvent leaves the washing zone, therefore, presents an extraordinary sensitive detection system by which the rate of loss of water from the system to the garments is used as an indicator of the regain state of the garments.

The factors which influence the differential rate of water adsorption by the garments from the solvent stream are: soap concentration, solvent temperature, rate of interchange of solvent between the cylinder and the washing wheel, and rate of solvent flow through the washing zone. However, these are constant factors which are determined by an examination of the overall drycleaning system. Once these factors are established, the moisture differential is solely a function of garment regain and amount or weight of garments in the wheel. It has been found that adequate control and cleaning values are usually attained within the range of 4 to 16 ounces of water per 50 gallons of solvent per minute of solvent flow through the washing zone.

In general, the electrodes of the present invention can be fabricated from any electrically conductive metal inert to the particular solvent. Usually, metals such as stainless steel, copper or brass can be utilized. Solid or hollow rod may be advantageously employed for the inner electrode while hollow pipe is used as the outer electrode.

The following example for controlling the amount of moisture addition to a cleaning system is presented to facilitate a better understanding of the invention. It will be noted that the RH of the garment phase will not exceed about 75% although the RH of both the solvent and the garments are not necessarily the same. Indeed the solvent entering the washer during the on-position of the meter injection will contain free emulsified water. The term RH or relative humidity as employed in the present specification may be defined as the ratio of the vapor pressure of water in a solvent (or garment) to the vapor pressure of pure water at the same temperature as that of the solvent (or garment). The degree of value of relative humidity is expressed as percent. RH values herein above about 75 may be defined as free water and RH values below about 75% may be defined as bound water, when equilibrium is reached.

EXAMPLE 1 Utilizing the flow diagram of FIG. 1, 30 gallons of perchloroethylene solvent which circulates at a rate of 30 gallons per minute between the filter and washer during the washing cycle are added to the washer unit of 30 pound garment capacity. When the RH of the cleaning system is less than 60%, water is injected into the solvent line entering the washer at the rate of 6 oz. per minute by the resistance sensitive control. The solvent is charged with 1% by volume of an anionic detergent comprising a magnesium phosphate ester admixed with monoisopropanolamine dodecylbenzene sulfonate. A 1% solution of this detergent in perchloroethylene will normally register a RH equivalent of 75 with about 0.15% total water and will not dissolve more than 0.2%0.4% water dependent upon temperature and impurities. Since 6 oz. of water per 30 gallons of solvent is equal to 0.15% water by volume, this 75% RH value is therefore exceeded by the incoming solvent.

The washer is next provided with a conductivity cell as shown in FIG. 1 measuring 1.5 feet in length and comprising an external electrode having an internal radius of 3.7 centimeters and an inner, concentrically mounted solid stainless steel electrode of 10 cms. in length and having an external radius of 1.7 centimeters as shown in FIG. 3. This cell has a cell constant of about and the above solvent control point for 60% RH solvent is equal to specific resistance of 637 megohms, and with the above cell a resistance sensitive relay controls at 2.5 megohms. When adding moisture to the washer there is provided excellent cleaning without fabric damage. With appropriate variation of the control point, use of detergent may vary from 0.754%.

EXAMPLE 2 Utilizing the flow diagram of FIG. 1, a 65 pound washer which contains approximately 250 gallons of perchloroethylene solvent during the washing cycle and having a flow of solvent through the washer of gallons per minute is used. Water is injected into the solvent line at the rate of 8 oz. per minute. A drycleaning detergent containing a mixture of sodium mahogany sulfonates and triethanolamine salt of dodecyl benzenesulfonic acid is added to the'solvent to supply 1.5% concentration therein. A load of 65 pounds of mixed fabrics of wool and silk is added to the washer which operated during a normal cleaning cycle of 15 minutes followed by extraction cycles of 3 minutes.

A self-cleaning conductivity cell comprising an external brass electrode having an internal radius equal to 3.7 centimeters and an inner concentrically mounted brass electrode having an external radius of 2.20 centimeters as shown in FIG. 3. This cell is found to possess a resistance of 3.0 megohms when 60% RH equivalent solvent is positioned or inserted into the solvent line between the washer and the filter. Moisture is then added to the solvent feed. It is terminated when the resistance drops 0.1 megohm. However, when the resistance increases to 3.1 megohms, moisture is again added. The moisture control is operated on and off periodically to meet the demand of the garments for merely minutes of the normal minute cleaning cycle for excellent cleaning results. In this run, the quality of the cleaning was so high that no garment required recleaning. In the usual practice, absent this type of control utilizing the conductivity cell of the invention, as much as or higher of the load had to be recleaned for quality drycleaning.

The original moisture content of the garments was equivalent to a 45% regain, but terminal regain at the end of the cleaning cycle is 60%.

Similar results are obtained utilizing petroleum solvents in conjunction therewith a mahogany soap detergent.

Visual examination of the garments after rinsing and extraction indicated that the garments showed no wrinkling of linings and complete removal of all surface stains.

Although the conductivity cell of the invention finds particularly usefulness in a drycleaning process, it can be generally employed in an environment which requires the detection of miniscule amounts of water, as for instance in detecting small quantities of water in gasoline or in oil while passing the material to be tested directly through the cell. The latter is self-cleaning and quite reliable.

A variety of oil-soluble solvents can be employed as, for instance, petroleum solvent, Stoddards solvent, carbon tetrachloride and trichloroethylene. The detergents admixed with the solvents can also be advantageously employed, such as the anionic detergents such as the petroleum sulfonates; or nonionics such as alkylaryl polyglycol ethers; or cationics. The concentration of these commercially available detergents may be widely varied but, in general, from 0.25% to 4% by weight of the 8 solvent is satisfactory for most operations. The detergent selected should be capable, at the concentration employed, of dissolving water in the solvent and reflect the presence of water by a change in specific resistance of the solvent.

We claim:

1. In the drycleaning of fabrics in a system wherein there is circulated through a washing chamber, a filter, a pump and conduits interconnecting the washing chamber, filter and pum a drycleaning solvent containing small proportions of water and drycleaning detergents capable of dissolving water in the drycleaning solvent, the improvement for rapidly detecting relative humidity of the solvent in the washing chamber comprising positioning immediately adjacent to the washing chamber at the outlet conduit a conductivity device through which all of the solvent from the washing chamber passes, said conductivity device comprising an outer tubular electrode and a concentrically mounted inner electrode, the internal radius of the outer tubular electrode being at least larger than the external radius of the inner electrode.

2. The method of claim 1 wherein the conductivity device is fabricated from a metal selected from the group consisting of stainless steel, copper and brass.

3. The method of claim 2, wherein the internal radius of the outer tubular electrode is at least larger than the external radius of the inner electrode.

4. The method of claim 3, wherein the drycleaning solvent is selected from the group consisting of:

(a) petroleum solvent,

(b) Stoddards solvent,

(c) carbon tetrachloride, and

(d) trichloroethylene.

References Cited UNITED STATES PATENTS 2,258,045 10/1941 Christie -183 3,101,240 8/1963 Mathews 8l42 3,263,224 7/1966 Berman et a1. 340-236 FOREIGN PATENTS 837,76 6/1960 Great Britain 3l762 LEON D. ROSDOL, Primary Examiner A. RADY, Assistant Examiner US. Cl. X.R. 3243 0 

